System and method for providing secure communication between network nodes

ABSTRACT

A network, network device and method is disclosed. A network of network nodes is disclosed in which the network nodes securely transmit communication signals using one or more spatial parameters unique to the network nodes. A dad positioning device capable of operating as a node in a network of the present invention is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority from utilityapplication Ser. No. 10/724,323, entitled “System and Method forProviding Secure Communication Between Network Nodes,” filed on Nov. 26,2003, which is further related to and claims priority from provisionalapplication Ser. No. 60/429,866, entitled “System and Method ofUtilizing Positioning Receiver Hardware for Network-Based TransceiverApplications,” filed on Nov. 27, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to data networks, and moreparticularly to a networked navigation-enabled system that providessecure communication between network nodes.

2. Related Art

While the development of navigation technology is a rapidly growingindustry, the value of being able to remotely obtain precise positioninformation has long been recognized. Numerous navigation applicationshave recently been recognized and systems relating thereto developed,with the result being that navigation technology has found its way intocars, boats, planes, construction equipment, farm machinery and cellularphones.

One of the most well developed navigation system is the globalpositioning system (GPS). In fact, GPS technology has matured to thepoint that virtually everyone, including scientists, sportsmen, farmers,soldiers, pilots, surveyors, hikers, delivery drivers, sailors,dispatchers, lumberjacks and fire-fighters can benefit from it. Variousapplications in which GPS has been used include location, navigation,tracking, mapping and timing.

Recently, the idea of network-assisted GPS systems has been introduced.However, these systems have only scratched the surface of theapplications that are possible by combining GPS technology with the fullfunctionality of network communications. Thus, there is a need in theart for a fully-networked navigation-enabled system. In addition to thenumerous possible applications in which a fully-networkednavigation-enabled system may be used, there is a further need in theart for positioning receiver hardware for network-based transceiverapplications that make use of navigation technology, such as GPS.

BRIEF SUMMARY OF THE INVENTION

A network, network device and method is disclosed. In one embodiment anetwork comprises a first network node and a second network node towirelessly communication with the first network node. In one embodiment,the first network node securely transmits communication signals to thesecond network node using one or more spatial parameters unique to thesecond network node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of a transponderconsistent with the principles of the invention.

FIG. 2 a is a schematic diagram of another embodiment of a transponderconsistent with the principles of the invention.

FIG. 2 b is a schematic diagram of yet another embodiment of atransponder consistent with the principles of the invention.

FIG. 3 a illustrates the simplified configuration and node interactionof a network, according to one embodiment.

FIG. 3 b illustrates the configuration and node interaction of anetwork, according to another embodiment.

FIG. 4 a depicts one embodiment of the functionality of a networkconsistent with the invention.

FIG. 4 b depicts another embodiment of the functionality of a networkconsistent with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

One aspect of the invention is to provide a network of data deviceshaving data representations of connectivity, network node position,and/or position topologies. In one embodiment, the data devices arenodes of the network and have the ability to share data with each other,as well as data from other sources connected to any of the networknodes. In yet another embodiment, a database of network topology isdistributed among the networked data devices such that changes in thenetwork state would be incorporated into that distributed topologicaldata representation.

In one embodiment, network nodes are addressable in terms of deviceidentification, connectivity topology and/or according to spatialparameters. Such spatial parameters may include position, velocityand/or other parameters associated with dynamic or static behavior.Addressing of the network nodes (which in one embodiment are datadevices) would enable communications of data and control information toonly the desired recipients separable by one or all of the parametersdefining the network topology characteristic.

One application of having spatially addressable network nodes is theability to define a method for secure communication. In one embodiment,communications between network nodes may be encrypted based uponpositional data, device ID or motional parameters increasing thedifficulty of deriving information from the message. In anotherembodiment, positioning signal qualities that enable a PVT (position,velocity, time) calculation to be made may be used in an encryptionscheme. For example, it is possible to reuse positioning signals (orportions thereof) to generate a new signal that can be correlated andtherefore demodulated only by the recipient in the intended positionspace. This spatial-correlation quality would enable a reciprocalcommunication link to be established between one or more qualifiedspaces, thereby diminishing the ability of the communication to becompromised by those outside the intended qualified spaces. Similarly,in another embodiment, the timing precision and synchronicity enjoyed bythe network may be used in traditional secure communications techniques,such as direct sequence spread spectrum (“DSSS”) or time hop spreadspectrum.

Another aspect of the invention is to provide a self-configuringnetwork. In one embodiment, the network can self-configure to add orremove network nodes on a connectivity basis. New nodes (e.g., datadevices) not previously on the network can join by protocol sharing withthe network after the connection is made, according to one embodiment.Similarly, the network may change the status of a node no longerconnected to an inactive status. In yet another embodiment, the lastknown parameters for a removed node are distributively stored aftercriteria for disconnection is met.

Another aspect of the invention is to provide a data positioning devicecapable of operating as a node in a network of the present invention. Inone embodiment, the data device is a radio frequency device havingintegrated into it means for wireless communication, remote controland/or encrypted communication for use in a network as described above.In yet another embodiment, the data device is a portable low cost andlow power device capable of receiving signals from navigation beacontransmitters and sensing environmental characteristics for calculationof position and dynamic behavior. Moreover, the data device may furtherbe capable of relaying that position and motion information to anotherdevice via a communications link, which may or may not be part of thenetwork of data devices.

As mentioned above, one aspect of the invention is to combinetransponder and receiver functionality. In the case of a direct sequencespread spectrum (“DSSS”) positioning receiver, given the fact that DSSSis based upon the reciprocal properties of modulo-2 addition, much ofthe receiver hardware may be shared with transmitter applications. SinceDSSS modulation and demodulation are reciprocal processes, the bi-phasemodulation of the carrier wave in a transmitter consists of multiplyingthe pseudo-random noise (PRN) sequence with the carrier wave. If we canmultiply that bi-phase modulated waveform with a synchronized, identicalPRN sequence, it is possible to duplicate the original carrier wave.Conversely, if we multiply the bi-phase modulated waveform with theoriginal carrier wave, we get the original PRN sequence as the result.These reciprocity characteristics lead us to the conclusion that thelocally-generated code can be used to “correlate” with the receivedbi-phase modulated code and yield a resultant carrier waverepresentation. So, in effect, the local code generator in a receiver isidentical to the associated transmitter code generator and therefore maybe used as a transmitter code generator itself.

In general, the sensitivity of a receiver is inversely proportional tothe bandwidth of that receiver, reaching a sensitivity maximum at thematched filter bandwidth and then degrading with increasingly narrowfilters. As a result, the time it takes to find a signal is inverselyproportional to the signal level and proportional to the frequencyuncertainty which sets the number of searches for the signal in thefrequency domain. Providing precise signal frequency assistance andsignal phase assistance reduces the number of signal search operationsnecessary to find the signal, which promotes prompt positiondetermination in signal-impaired conditions where the mandated narrowbandwidths result in longer detection times. Thus, another aspect of theinvention is to provide signal-based assistance information to increasethe ability of the data positioning device to find attenuatedpositioning signals using the characteristics of the data signal itself.

In one embodiment, the network design enables the network communicationssignals to be used as substitutes for the network node position signals(e.g., navigation beacon signals). Substitution for the network nodeposition signals requires that the communication signals have the sameessential characteristics required of the network node position signalsto facilitate position calculations to be performed.

As will be described in greater detail below, where the network nodesare navigation beacons, the positioning network may require a system ofequations derived from signals containing exact time, frequency andtime-tagged beacon position information. The beacons of such apositioning network may transmit signals with ranging properties thatenable signal phase to be distinguished against universal precise timein the receiver, thereby yielding the range from each beacon to thereceiver by factoring the speed of light into the calculus.

Since the proposed positioning network nodes are able to substitute formissing navigation beacon signals, they will also have the essentialcharacteristics for position calculation. Those signal characteristicsmay be representative of the assistance information that may be sent tothe positioning receiver. In one embodiment, the communications signalsare essentially a function of the navigation beacon signal, with thefrequency having a known relationship to the associated navigationbeacon signal, and the communications signal PRN being a known functionof the navigation beacon signal PRN. As a result, a positioningtransponder could derive information for finding weak signals from asubstantially stronger network communications link signal withoutrequiring that the information be modulated onto the signal as data.Thus, in one embodiment the positioning network may have uniqueintrinsic assistance information designed into its signals.

Referring now to the figures, FIG. 1 illustrates one embodiment of anintegrated transmitter/receiver unit consistent with the principles ofthe invention, which would enable continuous half-duplex communicationsand positioning. In particular, FIG. 1 depicts a twelve-channelpositioning transponder 100 capable of receiving the position signals 48by way of positioning antenna 2. In the embodiment of FIG. 1, thepositioning signals 48 are comprised of twelve CDMA (Code DivisionMultiple Access) positioning signals or CDMA communication channels.

In one embodiment, the position signals 48 may be comprised of one ormore navigation beacon signals, as required for receiver positiondetermination. While in one embodiment, the position signals 48 isgenerated from DSSS beacons, it should be appreciated that the positionsignals 48 may be provided by any navigation system beacon capable ofproviding positioning information.

Once received, the position signals 48 may be amplified by amplifier 4,which in one embodiment is a low-noise amplifier. Thereafter, filter 6may used to extract the components of the signal 48 at a desiredfrequency or range of frequencies. In one embodiment, filter 6 is aband-pass filter. It should further be appreciated that other methods ofsignal processing may be used.

Regardless of the front-end signal processing employed, switch 8 is usedto select the signal from either positioning antenna 2 or transponderantenna 10. When switch 8 is set to accept the position signals 48, RFdownconverter 22 may be used to down-convert the signal 48. In oneembodiment, RF downconverter is an RF to IF converter. Next, an Analogto Digital Converter (ADC) 24 converts the position signals 48 from ananalog signal to a digital signal before being provided tocorrelation/tracking circuit 50.

In one embodiment, correlation/tracking circuit 50 includescorrelator/demodulator 30, PRN code generator 36 and tracking mechanism34. However, it should be appreciated that the functions ofcorrelator/demodulator 30, PRN code generator 36 and tracking mechanism34 may be performed by other circuits that do not comprise thecorrelation/tracking circuit 50. However, for convenience, the followingdiscussion will assume the configuration shown in FIG. 1.

In one embodiment, tracking mechanism 34 performs clock generation,signal tracking and control functions. PRN code generator, based oninput from tracking mechanism 34, provides correlator/demodulator 30with PRN codes which are then used to correlate the received positionsignals 48 to the receiver locally generated signal. In anotherembodiment, the position signals 48 from multiple beacons may beprocessed using parallel hardware channels 1-n, where n represents thetotal number of position signals 48 and the total number ofcorresponding hardware channels. In this embodiment,correlation/tracking circuit 50 would be comprised of PRN codegenerators 36.sub.1-n and tracking mechanisms 34 _(1-n).

Controller 46 is part of the CPU system required for mostfirmware-controlled hardware. DSP subsystem 44 functions as a CPU tocontrol, calculate and schedule operations required for the transmitterand positioning receiver functions, while memory 42 is used by DSPsubsystem 44 to execute instructions required for transponder operation.However, it should obviously be appreciated that other processorconfigurations may be used. In addition, in the embodiment of FIG. 1,controller 46 passes either maximal length codes or Gold codes to PRNcode generator 36. Maximal length codes have the property of notrepeating until the 2^(n−1) clock cycle passes and they have correlationproperties defined by an up-slope and down-slope shape. Gold code, onthe other hand, can be generated by modulo-two adding two maximal lengthcodes together. While Gold code carries most of the characteristics ofthe maximal length code, it may have correlation responses besides themain one. These other correlation responses should be smaller than themain response for the codes used in the GPS.

Continuing to refer to FIG. 1, the transmission functionality oftransponder 100 will now be described. Transponder antenna 10 may beused to transmit and receive communication signals 52 with othertransponders. Given that transponder antenna 10 is capable of two-waycommunication, T/R switch 12 is used to select between transmit andreceive paths. Moreover, as with the position signals 48, a receivedcommunication signal 52 may be processed with amp 14 and filter 16. Whenreceipt of the communication signals 52 is desired, switch 8 is set toaccept the communication signals 52, which may then be provided to RFdownconverter 22. Sharing of RF downconverter 22 is enabled usingprogrammable frequency synthesizer 28, which may itself be shared forboth receiving and transmitting functions. While it may be economicallydesirable to use RF downconverter 22 and ADC 24 for both the positionsignals 48 and the communication signals 52, it should be appreciatedthat separate circuits for each may also be employed.

Transponder 100, like most positioning receivers which operate with DSSSsignal techniques, uses correlators and PRN code tracking loops forsignal de-spreading, synchronization and ultimately sensing thepseudo-range to the navigation system beacon being received on a givenchannel. The hardware to perform these functions, which in theembodiment of FIG. 1 is performed by correlation/tracking circuit 50,may be suitable for use in transmitter waveform generation. By makinguse of the reciprocity of the DSSS signal, it is possible to use thesame tracking mechanism 34 and PRN code generator 36 for input to acomplimentary code keying (“CCK”) modulator to generate a transmissionsignal that another receiver could in turn demodulate. Thus, in theembodiment of FIG. 1 having parallel hardware channels 1-n, trackingmechanisms 34 _(1-n) and PRN code generators 34 _(1-n) provide trackingloop and code generation data to CCK modulators 36 _(1-n) for use ingenerating transmittable communication signals 52. The number of CCKmodulators 36 _(1-n), may be added as needed up to a maximum numberdefined by the number of different code generators and trackingmechanisms available. As used herein, received communication signals 52refers to those signals which are received by the transponder overtransponder antenna 10 from other devices. Transmittable communicationsignals 52 refer to those signals that are generated by the transponder100 and which are sent to other devices via transponder antenna 10.

As mentioned above, transponder 100 may be used in a navigation beaconpositioned network or, alternatively, in a non-navigation beaconrelative-positioned network. In the embodiment of the beacon-positionednetwork, synchronization of the transmittable communication signals 52to the incoming position signals 48 may be employed. Tracking mechanisms34 _(1-n) are used for those applications of the transponder 100 whichrequire synchronization of the transmittable communication signals 52 tothe incoming position signals 48 from the navigation system positioningbeacon. In the embodiment where synchronization is required between thetwo systems, tracking loops of tracking mechanisms 34 _(1-n) that havebeen in a steady-state tracking mode for positioning would then“flywheel” at the rate of change for positioning and be switched overfor the transmission function and then switched back for positioningagain. In other embodiments, independent communications devices betweenpositioning and communications would enable simultaneous synchronizedoperations between the network and positioning system.

However, in applications which use non-beacon relative positioning, amaster transmitter in the network may be used to set the basic frequencyand phase of the network and the non-master elements (e.g., othertransponders 100) would then sample network signals for relativeposition and also switch to transmit the communication signals 52 whenrequired for data transmission, according to one embodiment.

In yet another embodiment, these transmittable communication signals 52may also double as ranging signals for the other receivers/transponders.Ranging signals employed by positioning or navigation systems may useseveral different methods of time tagging the signal for propagationtime determination from a transmitter to a positioning receiver. Thetime tagging enables the receiver to determine the transmit time whichis modulated onto the signal by the transmitter and compare thedemodulated time tag to the local time reference to determine the timeof propagation for the signal. This determined propagation time, scaledby the speed of light, may then be used to determine the range of thetransmitter to the receiver. In such a positioning network, the systemof known navigation beacon positions at their transmitted signal timetag yields a system of equations involving time, the transmitterpositions at time, and the range of the receiver to those transmitterknown positions. This system of equations usually has four variables andat least four equations which then can be solved for either a determinedor over-determined solution. The variables may include x, y, and zposition data, as well as time. By way of providing a non-limitingexample, one embodiment of a system of equations with four navigationbeacons would be as follows:

σ_(1r)² = (x₁ − x_(r))² + (y₁ − y_(r))² + (z₁ − z_(r))² + (c × t_(universal))²σ_(2r)² = (x₂ − x_(r))² + (y₂ − y_(r))² + (z₂ − z_(r))² + (c × t_(universal))²σ_(2r)² = (x₃ − x_(r))² + (y_(3 ) − y_(r))² + (z₃ − z_(r))² + (c × t_(universal))²                   ⋮σ_(nr)² = (x_(n) − x_(r))² + (y_(n) − y_(r))² + (z_(n) − z_(r))² + (c × t_(universal))²

where:

σ_(nr) ²=pseudorange of beacon n to receiverbased on code phasemeasurement

x_(n)=beacon n coordinate, x axis

y_(n)=beacon n coordinate, y axis

z_(n)=beacon n coordinate, z axis

c=speed of light

t_(universal)=best fit solved for universal time based upon bestposition fix result

This system of equations may be used to enable a best-fit solution ofreceiver position and time based upon received signal phase from fournavigation beacon signals.

In navigation systems where the positioning receiver can calculateposition, it may be preferable for there to be some receiver knowledgeof each of the navigation beacon's position and knowledge of the“universal time” of the transmitted navigation beacon signals. In caseswhere those navigation beacon positions are not known, it may bedesirable to convey the navigation beacon transmitter time-position tothe receiver. To that end, in one embodiment such data may be encodedonto the navigation beacon transmitter signal, thereby enabling thereceiver to demodulate the information and use it in the positioncalculation.

In one embodiment, a navigation beacon signal construct that adheres tothe description above may utilize a CCK BPSK (“Bi-Phase Shift Keying”)signal that has temporal properties useful for ranging measurements,while also enabling data modulation. In one embodiment, such a CCK BPSKsignal may be described mathematically as:

S_(beaconID)(t,prncode_(ID)(t),message_(ID)(t))=cos(ω_(c.ID)*t+π/2*message_(ID)(t)*prncode_(ID))

where the signal S_(beaconID) (t, prncode_(ID) (t),message_(ID) (t))consists of:

a function of time, t;

the PRN sequence, which may also function as the beacon ID, prncode_(ID)ε{−1,1};

a carrier wave, cos(ω_(c.ID)*t) with the angular carrier frequencyassociated with that particular beacon and therefore the associatedbeacon ID; and

a data message, message_(ID) (t) ε(−1,1), which represents a time markdefinition and the time—position function of the beacon that sent it.

Given that the PRN code has a cycle associated with the universal timeused by the navigation beacon network, and that the data messagecontains information about the universal time and positions of thebeacons, in one embodiment the receiver would be able to extractsufficient information to calculate its own position.

The data message and the PRN code may both have binary properties andhave values for this argument of “1” or “−1”. It is also possible toalter that PRN through a process known as CCK, which is a modulationwherein a PRN sequence is inverted when the message bit is a “logical 1”and not inverted when it is a “logical 0”. In order to mathematicallyrepresent this process, the data message and the PRN are considered asbi-polar signals; namely +1 and −1 for logical 1 and logical 0,respectively. As the BPSK process involves inversion of the signalcarrier for a “logical 0” and a pass-through for a logical 1, amultiplication of the carrier wave by the bi-polar representation willproduce a BPSK modulation.

A local representation of the received CCK BPSK code may be produced inthe receiver in order to enable detection of the transmitted signal andto demodulate any message that would be encoded upon it. In oneembodiment, the receiver can synchronize the local PRN to the PRNmodulation riding on the transmitted signal. This is accomplishedthrough the correlation properties of the PRN, which are at a maximum (anormalized +1) for correlation of like-PRN sequences which have the same“polarity sense” and which are in phase with each other. Similarly, thecorrelation properties of the PRN are at a negative maximum (anormalized −1) for correlation of like-PRN sequences which have theopposite “polarity sense” and which are in phase with each other.

In one embodiment, each PRN sequence has a length after which the PRNrepeats itself. This length, which may be referred to as the “PRNcyclicity”, may also help to define the correlation response to a PRNsequence that is unsynchronized with respect to a PRN replica that islocally generated. For maximal length PRN sequences, the unsynchronizedresponse may reduce to the normalized level of the value defined as“polarity sense*(−1/(code length),” where the polarity sense is +1 or −1when the two sequences are unsynchronized by one or more PRN clockperiods.

As a result, the correlation response between the received PRN and thelocally-generated PRN can be used as a measurement of synchronization byhaving a triangular response in delay space with the maximum correlationexcursion occurring when the two are synchronized. To that end, in oneembodiment, PRN synchronization uses these principles with ahypothesis-test loop where the locally-generated PRN is multiplied withthe receive signal and the response is measured. The phase of thelocally-generated PRN may be adjusted and the multiplication measurementresponse evaluated until an acceptable multiplication response level isattained. As the response is a triangular function in synchronizationspace, any loss of synchronization will result in a loss of correlationfrom the multiplication process and can be used to correct the PRN clockrate and/or PRN phase to maintain the maximum level of synchronization.

In order to detect advanced or retarded local PRN phase, two or moremultipliers may be used with a fraction of a PRN clock cycle signaldelay between them (e.g., ½ or ¼ the PRN clock cycle). In such a case,when the local code was advanced the advanced or “early” correlatorwould increase in response, and the “late” correlator would decrease inresponse. Conversely, when the local code was retarded from the receivesignal the “early” correlator would decrease in response, and the “late”correlator would increase in response. Thus, an “early response-lateresponse” term may be used to provide a feedback control signal whichcould be used to retard or advance the locally generated PRN replicarate towards maintaining receiver synchronization. This delay lock loop(DLL) technique may operate via controlling the locally generated PRNrate such that the received signal PRN phase is maintained between theearly and late correlators, where an equal response for both mayindicate the best possible synchronization.

Through the properties of a bi-polar multiply, it is also possible todemodulate the data from the received signal by multiplying it with alocally generated replica signal consisting of locally-reproducedcarrier wave multiplied with PRN. In another embodiment, the abovedescribed early and/or late correlator outputs may also be used for thissecond purpose. The local code phase, which is known by virtue of beingsynchronized with the received signal through the above described DLLprocess, may also provide the code phase measurement necessary forranging from the receiver to each of the respective navigation beacons.

In one embodiment, there may be an error rate above which the desiredposition information can no longer be extracted. Given that the desiredposition information is used to calculate position, this may cause apositioning sensitivity limitation. The code phase may be measured withan almost arbitrary level of sensitivity given sufficient localoscillator stability, sufficiently narrow bandwidths, sufficiently longintegration times, etc. It is possible to “assist” such a positioningreceiver with information that would normally be sent with the datamessage via some other communications link. For example, it is possibleto send over a separate communications link the range of code phasesexpected at the receiver position, the frequency of the navigationbeacon signal, the identifications (and PRN sequences therefore) of thenavigation beacons, etc. This would be useful in reducing the amount oftime it takes a receiver to measure the code phase since the narrowbandwidths necessary for weak navigation signal detection require aproportionately longer measurement period. Furthermore, because thebandwidths are narrow, the number of search attempts is increased withan indeterminate frequency of the signal.

While the information needed to perform these assistance functions maybe sent as explicit data over the communications link, in one embodimentthis information is implicit in the communication signal in question.That is, the PRN code cycle used by a transponder signal is related tothe navigation beacon signal PRN code cycle such that a receiver of thecommunications signal would have the PRN code timing of the “companion”navigation signal it is associated with. This is a form of code phaseassistance that is implicit in the signal, rather than an explicit datarepresentation of that code phase assistance. Likewise, the transpondercommunications signal frequency is deterministically related to theassociated “companion” navigation signal. Therefore, timing informationwould be part of the communications data message and would identify theuniversal time associated with the next code phase cycle commencement.

After controller 46 provides transmission data 62 to the CCK modulators36.sub.1-n, PRN code data 56 and correlator data 54 for a given channeln may be combined and summed by summers 38 for channels 1-n to provide aCCK signal 64. Thereafter, the CCK signal 64 may be up-converted inorder to change the basic CCK signal 64 frequency to the desiredfrequency of the transmittable communication signals 52. In theembodiment of FIG. 1, this is accomplished with the programmablefrequency synthesizer 28 which provides the required frequency toup-convert to the frequency of the transmittable communication signals52. The use of the programmable frequency synthesizer 28 for both theup-converter 26 and RF down-converter 22 follows from the fact that theup-conversion and down-conversion processes are reciprocal processes. Atransmittable communication signal 52 may be processed by amp 66 andfiler 68 before being transmitted via transponder antenna 10.

Moreover, transponder 100 has been shown with two separate antennaebecause it is likely that any transmitted communication signals 52 wouldbe much larger in amplitude than the position signals 48, which mayinterfere with positioning receiver operation. Also, some navigationbeacon systems are “radio transmission” protected to prevent emissions,intentional or unintentional, from interfering with the navigationsignals which may be small in amplitude. Because of this protectionagainst emissions, it may be desirable to choose other sanctionedfrequencies for the communications function of the positioning networktransponders. However, absent these factors, it should be appreciatedthat the position signals 48 and communication signals 52 may bereceived on the same antenna.

Referring now to FIG. 2 a, another embodiment of transmitter 100 isdepicted showing additional detail of correlation/tracking circuit 50.Moreover, in this single-data-channel embodiment, up-converter 26 isreplaced with RF mixer 70, which operates in conjunction with XOR gate75 and universal synchronous transmitter 80, as depicted in FIG. 2 a. Inparticular, PRN code data 56 is provided to universal synchronoustransmitter 80 and correlator data 54 is provided to XOR gate 75.Thereafter, using the output of the universal synchronous transmitter 80and the correlator data 54, the XOR gate 75 generates the CCK signal 64,according to one embodiment. In this embodiment, rather than useup-converter 26, the transmittable communication signal 52 is generatedby direct conversion using binary phase shift keying (BPSK) in the RFmixer 70 via multiplication of the CCK signal 64 (provided by the XORgate 75) with the local oscillator generated by the programmablefrequency synthesizer 28.

FIG. 2 b depicts a multi-channel embodiment of transponder 100 thatincludes a complex mixer for single-sideband up-conversion of the I andQ summed BPSK-CCK signals to a BPSK-CCK signal at the RF carrierfrequency. In this embodiment, communication bandwidth is maximized byhaving a communications channel associated with and sharing hardware andsoftware.

It should be appreciated that one of more of the components comprisingtransponder 100 may be implemented as integrated circuit(s), firmwareand even software. Moreover, one or more of the components comprisingtransponder 100 may be implemented by the chipsets marketed under thetradename of u-Nav Microelectronics Corporation, such as those chipsetshaving model number designations of uN8021B and uN8031B. The principlesof the invention may also be implemented by modifying the chipsetsmarketed under the tradename of u-Nav Microelectronics Corporation, suchas those chipsets having model number designations of uN8021B anduN8031B.

Referring now to FIG. 3 a, in which a network consistent with theprinciples of the invention is depicted. In particular, positioningnetwork 300 is shown comprised of a number of transponders 100 that areable to communicate with each other via communication signals 52, wheresuch signals may include data, position information, network topologyand/or commands. In addition, positioning network 300 (and each nodetherein) can communicate with other networks 320. Moreover, in theembodiment of FIG. 3 a, positioning network 300 receives positionsignals 48.sub.1-n from navigation beacons 310.sub.1-n, which in oneembodiment are DSSS satellite systems.

As mentioned previously, one aspect of the invention is to have networknodes that are addressable by physical characteristics. Thus, in theembodiment of FIG. 3 a, the nodes of positioning network 300 are thetransponders 100, which may each have knowledge of the network physicaltopology via communication signals 52. In one embodiment, the node-levelknowledge is maintained on a real-time basis. In another embodiment, theaddressability of the nodes (e.g., transponders 100) is based uponphysical quantities of either relative or absolute location, velocity orany combination thereof. Node identification can also be incorporatedinto the addressing scheme where each transponder 100 has its own deviceD.

As previously mentioned, one application of having spatially addressablenetwork nodes is the ability to define a method for securecommunication. To that end, in one embodiment, communication signals 48may be secure communications, encrypted with position authentication. Inanother embodiment, communication signals 48 may be spatially encodedaccessible only at a desired position. A spatially encoded signal couldbe demodulated only by a receiver at the proper position. In oneembodiment, this scheme could be utilized in “range-gated”communications in LPD applications and for spatially selectablecommunications and control functions. Similarly, other signal qualitiesmay be used to enable a PVT calculation to be made and used in anencryption scheme. Any combination of PVT outputs, or even raw receiverdata (e.g., code phase, etc.) could be used as a means of selectingintended recipients.

In another embodiment of spatial addressing, the positioning networkcould provide the necessary components to the desired signal fromseparate sources. By way of example, in a three-source case, ifnecessary information were available only if signal X at range of WXwere combined with signal Y at range WY and with signal Z at range WZ,only one point would provide the ability to receive and combine thethree signals with the proper relationships for extraction of thedesired information.

In yet another embodiment, positioning network 300 is a self-configuringnetwork. In particular, new transponders 100 can join the positioningnetwork by protocol sharing, according to one embodiment. Due to theself-configuration properties and distributed storage capabilities ofpositioning network 300, data relay becomes possible where network nodes(e.g., transponders 100) that cannot communicate directly, can pass datato each other through interstitial nodes. By use of this data-relayfunction, any node that receives position signals 48 of suitable qualityfor position fixing can pass the necessary data to the rest of thenetwork nodes that may be located in weak-position-signal conditions.Thus, one aspect of the present invention is to provide locationcapability for transponders 100 in weak-signal environments.

With respect to populating the network with network topology data,relative positioning of network nodes is possible where nodes calculateposition data from communication signals 52 that are received. Thetransmitting nodes on the network would have position knowledge, eitherabsolute or relative, and the triangulation techniques used commonly innavigation positioning receivers would operate in the same way on thenetwork transponder frequencies. Moreover, since all of nodes will haveposition signals 48 or communication signals 52 or both, it is possiblefor all nodes to be co-synchronized to each other. Thus, if positionsignals 48 are available to any node of the network, networksynchronization to the navigation beacon 310 system is possible.

In yet another embodiment, VLBI (Very Long Baseline Interferometry)measurements are facilitated without the need for additional hardware.VLBI techniques are typically used in some high-accuracy positioningsystems and involve the combination of the positioning data from two ormore receivers for the position calculation process. The required datamay be passed over the positioning network 300 between the nodes, whichin the embodiment of FIG. 3 a are the transponders 100. The use ofpositioning system time base may be used as a frequency reference forany systems combining other functions requiring precise frequencyreference.

As previously mentioned, one aspect of the invention relates to networkassisted positioning in which a communications link provides informationto assist a positioning receiver in acquiring the navigation signal. Inthis fashion, sensitivity and acquisition times of positioning receiverscan be improved. In one embodiment, this is accomplished by having thecommunications signals carry implicitly in their characteristics (e.g.,frequency, ranging code phase, etc.) a known relationship to theassociated navigation signal desired for acquisition. It is noteworthythat using these signal characteristics in this fashion enables positionassistance functionality to be performed without using datarepresentations of frequencies, code phases, and beacon PRN sequences.Relative positioning is also possible using triangulation techniques andcommunications signals for ranging measurements. In another embodiment,a communications channel may augment the navigation beacon 310 positionsignals 48.

In the embodiment of FIG. 3 b, no navigation beacons 310 are used.Rather, transponders 100 exchange positioning information as wasdescribed above with respect to FIG. 3 a, but on a relative basis.Similarly, network topology data is maintained on a relative basis.Thus, the positioning network 300 has knowledge of relative positionsbetween the communicating network nodes (position transponders 100) bymutual triangulation of the system of signals passing between the nodes(e.g., communication signals 52). If at least one absolute position isknown, the entire network is position self-aware.

FIG. 4 a depicts a simplified functionality diagram of a positioningnetwork 300 consistent with the principles of the invention. FIG. 4 b isa more detailed functionality diagram of positioning network 300 showingnumerous embodiments of the functions enabled by the invention.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. A positioning device whichreceives position signals from a plurality of navigation beacons andwhich is coupled to a network, comprising: a receiver portion; atransmitter portion; a processor coupled to the receiver portion andtransmitter portion; and a memory coupled to the processor to store oneor more instruction sequences, said instruction sequences to cause thepositioning device to communicate wirelessly with a second positioningdevice by securely transmitting communication signals to the secondpositioning device using one or more spatial parameters unique to thesecond positioning device, wherein the communication signals providefrequency and signal phase assistance used by the positioning device todetect attenuated positioning signals from said plurality of navigationbeacons.
 10. The positioning device of claim 9, wherein thecommunications signals are decodable by the second positioning deviceonly when the one or more spatial parameters match a correspondingspatial characteristic of the second positioning device.
 11. Thepositioning device of claim 9, wherein a position-velocity-time (PVT)calculation is used to encrypt the communication signals.
 12. Thepositioning device of claim 11, wherein the PVT calculation is used togenerate a new signal that can only be demodulated by a recipient nodelocated in an intended position.
 13. (canceled)
 14. The positioningdevice of claim 9, wherein the communication signals are synchronized tothe position signals.
 15. The positioning device of claim 9, wherein thecommunication signals are used as ranging signals for other positioningdevices.
 16. The positioning device of claim 9, wherein the positionsignals are usable for determining absolute positioning information forthe positioning device and the second positioning device.
 17. Thepositioning device of claim 16, wherein the communication signalsfurther comprise at least non-position data and absolute positioninformation.
 18. The positioning device of claim 9, wherein thecommunication signals substitute for the position signals in determiningposition information.
 19. (canceled)
 20. (canceled)
 21. The positiondevice of claim 9 wherein the position signals from a plurality ofnavigation beacons comprises position signals from the GlobalPositioning System (GPS).